This invention relates to apparatus for switching direct current (DC) electric power, and more particularly to such apparatus which is polarized yet bi-directional, i.e. it can switch current with either polarity, but its performance is better with one polarity of the current than with the other polarity.
DC power has been proposed for electrically powered vehicles in which the electricity is derived from a bank of storage batteries or other DC power source. In electric automobiles, a switch is provided between the DC power source and an electric motor, which drives the wheels of the vehicle. Weight, reliability and high DC voltage switching and interrupting capability are important considerations in developing the switching apparatus. Furthermore, relatively high direct currents must be switched which produce arcs when the contacts of the switch are opened, thereby requiring a mechanism for extinguishing the arcs.
Although current conducts in one direction between the source and the electric motor when the electric motors are driving the wheels, electrically powered vehicles also have a regeneration mode in which the current conducts in the opposite direction when the wheels are not being driven by the motor. Thus, the switch between the DC power source and the motor must be capable of handling switching and fault currents in both directions at high DC voltage and extinguishing arcs which may occur regardless of the direction of that current.